The operation of a power source generates heat. A heat transfer system, in communication with the power source, regulates the generated heat by absorbing and dissipating the heat from the power source. A gasoline powered internal combustion engine, for example, powers an automotive vehicle. Heat transfer fluids and systems dissipate the heat generated as a by-product of gasoline combustion, and ensure that the engine operates at an optimum temperature. Heat transfer fluids, which generally comprise water, glycol or glycol-water mixtures, are in communication with one or several metallic parts that are prone to corrosion. Thus, several corrosion inhibitors are added to the heat transfer fluid in order to protect the metallic parts from corrosion.
Aluminum is an example of a metal that, along with its alloys, can be used in the manufacture of several components of the heat transfer system such as heat exchangers which include but are not limited to radiators, condensers, evaporators, heater cores, intercoolers, charge air coolers, oil coolers, and the like. These components can be manufactured using several techniques, one advantageous technique being brazing, wherein the individual components are permanently joined together with a brazing alloy. Generally, brazed heat exchangers are lower in weight and are able to radiate heat better than heat exchangers formed by mechanical expansion.
Controlled atmosphere brazing (“CAB”) is a method used by the automotive industry for making brazed aluminum components for a heat transfer system. CAB provides for improved production yields, lower furnace maintenance requirements, greater braze process robustness and lower capital cost of the equipment employed. However, in a CAB process, a fluxing or flux agent is applied to the pre-assembled component surfaces to be jointed. The fluxing agent is used to dissociate or dissolve and displace the aluminum oxide layer that naturally forms on aluminum alloy surfaces. The fluxing agent is also used to prevent reformation of the aluminum oxide layer during brazing and to enhance the flow of the brazing alloy. Fluxing agents generally include halide anions, such as but not limited to, alkaline metal or alkaline earth metal fluorides or chlorides. One non-limiting example of a fluoride based flux is NOCOLOK™. NOCOLOK™ fluxes are widely used in the automotive industry for brazing aluminum and/or aluminum alloy surfaces.
After brazing, the residual flux on aluminum and/or aluminum alloy surfaces can leach out halide ions, such as but not limited to, fluoride ions, as well as other species from flux residue components in different stage of oxidation, such as but not limited to potassium, sodium, aluminum, zinc ions. The leached out halide ions and flux residue components can lead to localized corrosion on the metal substrates when it is in contact with a heat transfer fluid in the heat transfer system. This disadvantageous localized corrosion resulting from the residual flux can occur in the presence of several commercial heat transfer fluids, including but not limited to those based on organic acid technology (“OAT”), or hybrid organic acid and silicate (“HOAT”) or traditional inorganic acid-silicates (IAT) based heat transfer fluids.
Therefore, there exists a need to provide heat transfer fluids intended for use in heat transfer systems comprising brazed metals or metal alloys such as brazed aluminum, which provide corrosion protection from residual fluxing agents, specifically from those comprising halide anions, and more specifically from those fluxing agents comprising fluoride anions.